1. Field of the Invention
The present invention relates to a membrane coupled activated sludge method and apparatus operating anoxic/anaerobic processes alternately for removal of nitrogen and phosphorous. In particular, the invention relates to a method for treating sewage, wastewater, filthy water, etc. wherein nitrogen and phosphorous together with organics in the sewage, wastewater, filthy water, etc., can be simultaneously removed with economic and efficient manners using a membrane coupled activated sludge apparatus comprising an anoxic/anaerobic alternating-type reactor with an intermittent internal recycle at a time interval and an aerobic reactor having a separation membrane of a submerged-type and operating continuously, and more particularly to a method for treating sewage, wastewater, filthy water, etc. for simultaneous removal of nitrogen and phosphorous wherein an operation thereof is easy and efficient, a capacity thereof is high and the method is economic due to the reduced operating costs with performing measurement and control of a recycle rate, a recycle time of alternate operation of the anoxic and anaerobic process, an amount of sludge, an amount of aeration and an operation of a blower for an intermittent membrane cleaning.
2. Background of the Related Art
When nitrogen and phosphorous contained in a sewage, wastewater, filthy water, etc. are discharged without any treatment, they may cause eutrophication in rivers and lakes and thus exerts bad influences on water resource and water ecosystem. Especially, when an infant drinks water containing a large quantity of nitrate nitrogen, cyanosis can be caused, so that a measure for this is required.
Accordingly, in order to treat nitrogen and phosphorous of which regulations are being intensified, various advanced treatments have been suggested. As representative treatments, there have been biological advanced treatments such as MLE (Modified Ludzack-Ettinger), UCT (University of Cape Town), MUCT (Modified University of Cape Town), VIP (Virginia Initiative Plant) and the like.
However, the above treatments have a disadvantage of very complex operation since the treatments usually use a plurality of reactors and internal circulation pumps and it is difficult to maintain optimal conditions for removing nitrogen and phosphorous according to the treatments. Further, the above treatments have a problem that it is hard to maintain a concentration of microbes to be high since a solid-liquid separation between microbes and treated water is carried out by gravity sedimentation in a settling tank. In addition, according to the above treatments, since a bulking phenomenon of microbes occurs by shock loads such as change of inflow load and inflow of toxic substances, the quality of the treated water is poor and an efficient treatment is difficult due to a loss of activated microbes. Further, the treatments require large sites since it is necessary to equip at least two independent reactors and a terminal settling tank according to the treatments, so that they are not suitable for small and medium sized sewage/wastewater advanced treatment.
In order to solve the above problems, various sewage/wastewater advanced treatment methods using a separation membrane in solid-liquid separation have been attempted. However, in this case, a plurality of reactor should be also arranged for such advanced treatments and the removal of nitrogen is difficult.
As one of the prior treatment methods, there is known a “drainage treating method.” According to this method, a first treatment tank inducing nitrification and denitrification through an intermittent aeration and a second treatment tank having a submerged-type separation membrane for solid-liquid separation are provided to remove nitrogen and to carry out a continuous suction filtration (Japanese Patent Publication No. Hei 7-100486). However, this method cannot remove phosphorous efficiently since an anaerobic condition for removing nitrogen cannot be made. In addition, since the second treatment tank is separately provided to carry out the continuous suction filtration, an additional aeration for the second treatment tank is required to prevent the separation membrane from being contaminated. As a result of that, energy costs for the aeration are needed twice.
As another example of the prior art, there is known “apparatus and method for biologically removing nitrogen and phosphorous using submerged-type separation membrane.” According to this method, anoxic, anaerobic, aerobic and deaeration tanks are sequentially installed to induce simultaneous removal of nitrogen and phosphorous (Korean Patent Publication No. 2002-44820). However, in this case, the anaerobic tank also should be additionally provided to remove phosphorous. In addition, when treating sewage having a small C/N ratio, most of carbon sources are used to remove nitrogen in the anoxic tank installed at the front end, so that the carbon sources required for phosphorous release are deficient in the anaerobic tank and thus the method has a limitation in the phosphorous removal.
Accordingly, needed is a sewage/wastewater advanced treatment method having a structure simplified by reducing the number of the reactors and required pumps and capable of carrying out a continuous treatment while treating nitrogen and phosphorous simultaneously and improving a quality of treated water.
Meanwhile, in recent years, as a computer technology develops and a reliable measuring instrument appears, researches on diagnosing sewage/wastewater treating procedures and performing a process control are being carried out by monitoring a sewage/wastewater dump and using data obtained from the monitoring.
It is called a measurement and control that quantitative and qualitative data of a process are perceived with a measuring equipment so as to monitor a process situation and an instrument or apparatus is made to operate under optimal situations using the data.
One example of the measurement and control is a blower operation of attaching a timer and setting operation and non-operation times of the blower in a continuous batch reactor.
In addition, known are methods of performing a real time measurement. For instance, there have been developed control methods of using absolute values or variations according to time of oxidation-reduction potential (ORP), hydrogen ion concentration (pH) and dissolved oxygen (DO) (U.S. Pat. Nos. 5,303,308A, 5,624,565 A, 6,093,322A and 6,527,956B1 and JP 1994-055190).
Further, in a case of a continuous reactor, known are methods of measuring DO to control an air amount supplied to an aerobic tank (U.S. Pat. No. 4,537,682A). Also, it is reported a method of calculating a difference of ORP values between those of inflow water and an anoxic tank to control a recycle rate (U.S. Pat. No. 5,733,456A).
However, since the above measurement and control methods according to the prior art have been developed to be suitable for the corresponding sewage/wastewater treating methods, it is needed to develop a new measurement and control process as well as a new sewage/wastewater advanced treatment process.